A method of this kind is known from American U.S. Pat. No. 4,925,388, which describes a furnace in which, for cooling purposes, a gas is guided through the furnace either from above or from below. The direction of flow of the gas alternates, and this alternating movement is controlled by a number of valves. The gas moves in the space between the heating element and the core tube and in the space between the heating element and the insulation arranged at a distance therefrom. The air or other gas which is used as cooling medium is discharged via a fan.
It has been found that the discharge of such gases into a discharge system of a relatively large installation is accompanied by major drawbacks, since by definition these gases are hot and consequently can damage a discharge system of this kind, in particular if it is composed of plastic components. Moreover, harmful substances may be present in the gases.
The object of the present invention is to avoid this drawback and to provide a method which, on the one hand, allows rapid and uniform cooling and, on the other hand, does not subject the gas-discharge system to further loading.
An aspect of the invention involves a method for cooling a furnace having a core tube that has an elongate boundary wall and is configured to accommodate wafers for processing the wafers in a treatment atmosphere. The furnace includes a cooling chamber defined between the elongate boundary wall and an outer casing of the furnace, wherein the outer casing includes a heating element and has first lateral, circumferentially spaced openings in proximity of a first end of the outer casing and second lateral, circumferentially spaced openings in proximity of a second end of the outer casing. Cooling gas is supplied through one of the first and second lateral, circumferentially spaced openings to a region of one end of the cooling chamber and provides for a cooling atmosphere. The cooling gas is guided along the cooling chamber with a uniform distribution of flow and discharged through one of the first and second lateral, circumferentially spaced openings from a region of an opposite end of the cooling chamber. A direction of flow of the cooling gas is periodically reversed during cooling, wherein the cooling gas is guided along an essentially closed circuit so that the cooling gas is preserved and so that the cooling atmosphere is separated from the treatment atmosphere. A liquid-gas heat exchanger cools the cooling gas.